This invention generally relates to measuring and alignment procedures and, in particular, relates to internal component alignment within a turbomachine casing.
A turbine casing for a large turbomachine is usually split along a horizontal joint to form casing halves; an upper casing half and a lower casing half. Within the turbine casing there are certain stationary internal components which minimize the axial flow of motive fluid such as packing rings, diaphragms, and other annular surfaces about the rotor surface. Generically, these devices may be referred to as packing ring holders. During the assembly of the turbine a packing ring holder half is positioned into each casing half. Thereafter a rotor is positioned into the lower casing half. One aspect of the present invention deals with aligning the packing ring holder with the surface of the turbine rotor. There is a radial clearance between the rotor surface and the packing ring holder inner circumference which extends along the length of the holder inner circumference. It is important that the rotor be exactly positioned within the lower packing ring holder half. Thereafter the upper casing half is lowered onto the lower casing half and bolted into place.
The radial annular clearance between a rotor surface and an annular packing ring is necessarily very limited to prevent excessive axial leakage of motive fluid and consequent decrease in machine efficiency. This clearance may be expressed in terms of mils. If the clearance is too great there is an increase in axial steam leakage. If the clearance is too slight then there is a chance that a shaft rub could cause damage to either the shaft or a packing ring which terminates the inner circumference of a packing holder. This means that extraordinary care must be taken in order to properly position the rotor relative to the surrounding annular packing ring holder. Relatively simple measurement devices such as mechanical gauges or shims have been utilized as well as sophisticated electronic or telemetric methods. The present invention is a relativey simple yet accurate method of positioning a turbine rotor within a turbine casing.
In carrying out the method of the present invention, means had to be devised for measuring the requisite radial clearance in a relatively restricted area. Means have been invented for inserting a plurality of space proximity probes between the rotor surface and the packing holder inner circumference for measuring the radial clearance therebetween at certain predetermined locations around the rotor surface. The packing holder is adjusted until the rotor surface is equally distant from the measuring probes. Adjustment means for altering the packing holder position are illustrated; for example, in U.S. Pat. No. 3,861,827 to Peabody et al. It is desirable that the method and apparatus of the invention be available for both factory and field installation.